Sydney, Dec 23: Australia remained on high alert after seven people were arrested on Friday for allegedly planning a Christmas Day terror attack.

Security officials raided several properties in Victoria state, arresting five self-radicalised men aged between 21 to 26 years old for allegedly preparing a multi-
mode terror attack targeting downtown Melbourne using explosives and other weapons, possibly on Christmas Day, Xinhua news agency reported.

Two others, a 20-year-old woman and 26-year-old man were also arrested, but later released without charge.

"In terms of events that we have seen over the past few years in Australia, this certainly concerns me more than any other event that I've seen," Australian Federal
Police Commissioner Andrew Colvin told reporters in Sydney on Friday.

Melbourne's iconic Flinders Station, Federation Square and St Paul's Anglican Cathedral were the likely targets, the police said.

Australian authorities have remained on alert for a Christmas Day plot following Indonesia's Special Detachment raids that killed three terrorism suspects in West
Jakarta on Tuesday and recent attacks in Berlin where a truck have rammed into large celebratory gatherings killing 12 people.

"Islamist terrorism is a global challenge that affects us all. But we must not be cowed by the terrorists," Australian Prime Minster Malcolm Turnbull said. "I can assure all Australians that our police services right across the country, our intelligence agencies right across the country, and around the world, are at the
highest state of alert."

Police presence will be enhanced across Australia for public events, such as the New Years Eve fireworks in Sydney, Christmas Eve carols in Melbourne and the Boxing
Day Test at the Melbourne Cricket Ground (MCG).

Australia raised its terror alert in September 2014 and since then has strengthened security and passed a number of anti-terrorist laws to prevent attacks on its
territory, which has been the scene of isolated attacks.